1. Field of the Invention
The present invention relates to an S/N enhancer which utilizes a magneto-static wave device for increasing a signal to noise ratio (S/N) of a high frequency electro-magnetic wave signal (e.g. a micro-wave signal) by utilizing the saturation of a magneto-static wave converted from an electro-magnetic wave, which propagates through a thin film of ferri-magnetic material (e.g. a ferrite thin film), so as to efficiently improve the S/N of the original signal without any increase of insertion loss thereof in a transmission path.
2. Related Art Statement
The magneto-static wave propagating through the ferrite thin film in the magneto-static wave device of this kind, particularly a superficial magneto-static wave propagating along the film surface thereof, is readily saturated even in a small amplitude region thereof. So that, the device of this kind presents a non-linear input-to-output characteristic for an electro-magnetic wave which has an electric power as large as that of the magneto-static wave converted therefrom exceeds the threshold of saturation, while it presents a linear input-to-output characteristic for the electro-magnetic wave which has an electric power as small as that of the magneto-static wave converted therefrom which does not reach to the threshold of saturation.
In this connection, a conventional S/N enhancer has been developed in which, according to the utilization of the magneto-static wave device presenting the aforesaid input-to-output characteristics, noise components among an input electro-magnetic wave which don't reach the threshold of saturation are entirely consumed through the conversion into the magneto-static wave, while signal components which do exceed the threshold of saturation are passed through, so as to increase the signal-to-noise ratio. However, according to this conventional development, a sufficient increase of S/N could not be attained because of the impedance variation caused as described in detail later and the like.
In connection with the above, another conventional S/N enhancer has been developed utilizing the magneto-static wave. In such a S/N enhancer, two channels are provided, which respectively present the aforesaid non-linear and linear input-to-output characteristics, by replacing the order of series connection with each other between a magneto-static wave device and an attenuator and are separately supplied with the same input electro-magnetic wave. The respective outputs of these two channels are mixed with each other, such that noise components thereof are canceled by each other, so as to increase the signal-to-noise ratio thereof.
However, in these conventional S/N enhancers utilizing magneto-static waves, because the input-to-output characteristic is based on an extremely low threshold of saturation of the magneto-static wave propagating through the ferrite thin film, as for the channel presenting the linear input-to-output characteristic, the attenuator is prefaced to prevent the saturation of the magneto-static wave device. Hence, the output level of the mixed electro-magnetic wave, from which noise components are canceled, is extremely lowered. As a result, the insertion loss of the S/N enhancer is extremely increased. In addition, another defect of this S/N enhancer is that when the electric power levels of the electro-magnetic waves individually supplied to the magneto-static wave devices in the two channels differ greatly from each other, a discrepancy is caused between respective phase characteristics thereof, so that a electro-magnetic-wave having an excessively large electric power can not be supplied to this S/N enhancer. Consequently, the prevention of the effect of the discrepancy of the phase characteristic without any increase of the insertion loss is the conventional problem to be solved as for an S/N enhancer of this kind utilizing magneto-static waves.